Color images can be electrophotographically or inkjet printed on transparencies. Such colored images are then projected onto a screen by an overhead projector. When such transparencies are electrophotographically color printed, many of the toner particles deposited on the transparency are only partially fused to the transparency. This partial fusion results in high surface roughness on the side of the transparency printed with the toner. When the images created by the toner particles are projected onto a screen, there is significant light scattering that gives a gray look to the projected image. This light scattering phenomenon and the resultant grayish cast in the projected image is not only caused by poorly fused toner particles. The presence of variations in toner layer thickness (up to 20 xcexcm) also contributes to this phenomenon.
Solutions have been previously proposed to alleviate the above light-scattering problem. One solution is to apply a single sided, transparent, pressure-sensitive adhesive laminate to the printed side of an electrophotographically printed transparency. Such pressure-sensitive adhesive laminates have the disadvantage of being relatively thick in comparison to the transparencies. Therefore when the laminate and transparency layers adhere together, large air bubbles become easily trapped between the two layers.
Another solution to the light scattering problem is to apply an oil coating to the printed side of the electrophotographically printed transparency. If the oil coating refractive index matches the refractive index of the toner resin on the transparency, light scattering decreases. However, such an oil coating gives the coated side of the laminate a sticky and/or greasy feel.
Yet another solution is laminating a second transparency to the printed side of the electrophotographically printed transparency. The disadvantage of this solution is that, like the pressure-sensitive adhesive laminate described above, laminating a second transparency adds a layer of significant thickness to the electrophotographically printed transparency. This other layer is very likely to trap air bubbles. Furthermore, the significant relative thickness of the second transparency requires higher temperature and pressure and longer exposure time to fuse the transparency to the printed side of the electrophotographically printed transparency.
In Japanese Laid-Open Patent Application (KOKAI) No. 80273/1988, specific examples of methods of smoothing unfused color toner particles on a transparency are given. Specific examples of such a smoothing method include:
(1) one wherein the toner particles are fixed at a temperature at which they are sufficiently fused
(2) one wherein the toner particles are fixed by using a solvent such as toluene;
(3) one wherein the fixed image is ground; and
(4) one wherein a transparent paint not dissolving the toner is applied onto the fixed image.
In the three patents of Takeuchi et al. (U.S. Pat. Nos. 5,032,440; 5,229,188; and 5,352,553)(Assigned to Canon), Column 1, line 50, to Column 2, line 46, the disadvantages of the above methods of Japanese Laid-Open Patent Application (KOKAI) No. 80273/1988 are discussed as follows:
xe2x80x9cIn the case of the above-mentioned method (1) wherein the fixing is effected at a high temperature by using a fixing roller, when a half-tone portion having a small amount of toner particles is intended to be smoothed, a so-called offset phenomenon occurs in a portion having a large amount of toner particles (e.g., a black portion wherein cyan toner, magenta toner and yellow toner are co-present). When a non-contact-type heat fixing device such as oven is used, the transparent film is waved and a considerable period of time is required in order to obtain sufficient transmittance.
xe2x80x9cIn the case of the above-mentioned method (2) using a solvent, when the toner particles are sufficiently fluidized by use of a solvent so that those constituting a half-tone portion lose their particulate property, distortion or flow of an image occurs in a high-image density portion.
xe2x80x9cIn the case of the above-mentioned method (3) using the grinding of an image, the transmittance is increased in a portion having a relatively large amount of toner particles, but the particulate property of those constituting a low-image density portion is not sufficiently removed. As a result, it is difficult to remove shadows due to the peripheries of the toner particles.
xe2x80x9cIn the case of the above-mentioned method (4) wherein a transparent paint not dissolving toner particles is applied onto a toner image, clear boundaries or interfaces can sometimes be formed between the toner particles and the paint, whereby black absorption occurs in a reflection-type overhead projector due to light scattering caused by the boundaries.
xe2x80x9cIncidentally, in order to enhance the color reproducibility in a full-color image, there may be used a binder resin for color toner such that it provides high fluidity and a low-viscosity state (about 104 poise) at the time of fixing. In order to fix the low-viscosity toner without causing high-temperature offset (i.e., an offset phenomenon such that when a color toner image formed on the transparent laminate film is fixed by a fixing means such as heat pressure roller, the melted toner image adheres to the heat pressure roller), a dimethylsilicone oil having a viscosity of 100-1,000 cs (centistokes) is ordinarily used as a supplemental release agent. Accordingly, in the case of the above-mentioned method (4), when the dimethylsilicone oil is used, the paint cannot sufficiently adhere to the transparent film, where it causes new image unevenness.xe2x80x9d
The Takeuchi et al. patents treat the light-scattering problem by having a transparent laminate film, including at least a first transparent resin layer comprising a transparent resin having a heat-resistance, and a second transparent resin layer disposed thereon comprising a transparent resin, wherein the transparent resin of the second transparent resin layer has a compatibility with a binder resin of a toner to be fixed thereon, and has a larger elasticity than that of the binder resin of the toner at a fixing temperature of the toner.
Thermal transfer overcoats (TTO) also known as transfer ribbons, thermal transfer ribbons, hot stamping foils, roll foils, and transfer printing foils, are used by a number of different industries. Thermal transfer printing is a popular method for producing on-demand printed images, barcodes, receipts, and labels. This market uses solid fill colored ribbons to create images on a base media, and potentially a clear ribbon to provide added durability improvement.
The present invention relates to a method of applying a protective overcoat to a surface of a printed transparency to create a transparency with a protective overcoat, comprising: applying heat and pressure to a donor web having a carrier side comprising carrier ribbon material and a transfer side comprising protective overcoat material, wherein the heat and pressure facilitate release of a section of the transfer side from adhering to the carrier side of the donor web and facilitate transfer of the section of the transfer side to adhering to the surface of the transparency.
The present invention also relates to an overcoat for a printed transparency and the transparency itself to which the overcoat is applied, the overcoat on the transparency being made by the above-described method.
The present invention also relates to a donor web providing a protective overcoat to a printed transparency, the donor web having:
a) a carrier side comprising a carrier ribbon material and a lubricant layer as an exterior layer preventing wear of a surface of a heating element or pressing element, the surface coming in contact with the carrier side of the donor web;
b) a transfer side comprising a protective overcoat material, a release layer as an interior layer adjacent to the carrier side, the release layer facilitating release of the transfer side from the carrier side; and an adhesive layer as an exterior layer of the transfer side, the adhesive layer enhancing adhering of a section of the transfer side to form the protective overcoat on the transparency.
The present invention also relates to an apparatus comprising a donor web having a carrier side comprising carrier ribbon material and a transfer side comprising protective overcoat material, and a means of applying a protective overcoat to at least one surface of a printed transparency, by applying heat and pressure to the donor web, wherein the heat and pressure facilitate release of a section of the transfer side from adhering to the carrier side of the donor web and facilitate transfer of the section of the transfer side to adhering to the at least one surface of the transparency.